The process forming the object of the present invention is applicable to the treatment of conventional crude oil residues, either straight-run or vacuum residues, as well as to the treatment of heavy or extra-heavy topped oils such as obtained, for example, from the fields of FAJA PETROLIFERA in Venezuela or from the fields of ATHABASCA in Canada. By extension, the claimed process will also be advantageously used for the treatment of straight-run or vacuum residues issued from another thermal or catalytic previous treatment such as visbreaking, hydrovisbreaking, thermal treatment in the presence of a hydrogen donor solvent, various catalytic hydrotreatments with more or less extensive conversion of the treated charge.
These various charges are characterized by the fact that they contain resins and asphaltenes which are organic products of high molecular weight containing a large proportion of S, N and O heteroatoms, with which metals, particularly nickel and vanadium, are complexed.
The disadvantages of these asphaltenes and resins in refining operations are well known, as well for catalytic as for thermal processes.
These disadvantages are related to their high content of heteroatoms but mainly to their low H/C ratio and to the presence of nickel and vanadium as complexed metals.
For catalytic cracking, in the presence of zeolite catalysts, for example, the presence in the charge of compounds of said type produces an increase of the coke deposit on the catalyst with the liability of rupture in the unit thermal balance and of increase of the regeneration temperature up to such values that zeolites quickly loss their crystallinity; the presence of nickel results in the deposition of said metal on the catalyst with, as a consequence, an increased production of uncondensable gases and of hydrogen and an increase of the coke deposit. Now, vanadium, when deposited on the catalyst, may also form with the zeolites exchanged with rare earths, constituting the active phase of the usual catalysts for this type of reaction, a mixed compound producing a loss of crystallinity and, accordingly, a loss of activity.
In hydrotreatment operations, such catalyst poisoning is well known. The progressive deposition of nickel and vanadyl sulfides on such active agents as sulfides of metals from group VI A (molybdenum or tungsten) promoted by sulfides of metals from group VIII (nickel and cobalt), results in a progressive decrease of the desulfurizing, denitrogenating and hydrogenating activities of these catalysts.
In hydrocracking, the asphaltenes content, determined by precipitation with heptane according to the French Standard AFNOR NFT 60115, must be almost undetectable in order to avoid the quick poisoning of the catalyst acid sites with subsequent coke production.
In visbreaking, the severity of the operating conditions also depends on the content of said asphaltene products and on their intrinsic stability. For a given charge, a too high severity, expressed in terms of excessive temperature and (or) maturation time, results in the coagulation of the partially cracked asphaltene molecules with production of colloidal micelles which tend to settle during storage and to plug the filters of the use apparatus.
All these disadvantages have induced refiners to make searches in view of selectively separating the asphaltene and resin compounds from the oil fraction containing them. This separation, called deasphalting by solvent, consists of breaking the existing equilibrium between asphaltenes and the maltene surrounding medium by addition of a solvent which decreases the viscosity and, overall, the interfacial tension of the oil medium. The recommended solvents are generally light paraffins or (and) olefins of 3, 4, 5, 6 and (or) 7 carbon atoms. In fact, the light paraffin acts, with respect to asphaltenes and optionally with respect to resins, as an anti-solvent. Asphaltenes and resins are rejected outside from the oil medium as a separate phase, and this to a greater extent as the density and the interfacial tension of the solvent plus oil medium are lower. Consequently, the "asphalt phase" yield and the quality of the deasphalted oil, for a given charge, relate to the following parameters and variables: nature of solvent, proportion of solvent, temperature and pressure, but they also depend to a very large extent on the characteristics of the selected technology.
The process according to the present invention thus relates to deasphalting of hydrocarbon solvents comprising paraffinic or olefinic hydrocarbons having 3 to 7 carbon atoms. However, the hydrocarbon solvent is used in such a manner as to obtain high yields of an oil of very high grade with a minimum solvent content and to make possible its extrapolation to industrial units having annual treatment capacities in single line ranging from about 2 to 4 millions of tons.